1. **State the problem:** Find the maximum and minimum points of the function $$f(x) = x^3 + 3x^2 - 4x$$ and describe its graph.
2. **Find the derivative:** To find critical points, compute $$f'(x)$$:
$$f'(x) = 3x^2 + 6x - 4$$
3. **Set the derivative equal to zero:** Solve for $$x$$:
$$3x^2 + 6x - 4 = 0$$
Divide both sides by 3:
$$x^2 + 2x - \frac{4}{3} = 0$$
4. **Use the quadratic formula:** For $$ax^2 + bx + c = 0$$, $$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
Here, $$a=1$$, $$b=2$$, $$c=-\frac{4}{3}$$.
Calculate the discriminant:
$$\Delta = 2^2 - 4 \times 1 \times \left(-\frac{4}{3}\right) = 4 + \frac{16}{3} = \frac{28}{3}$$
5. **Find the critical points:**
$$x = \frac{-2 \pm \sqrt{\frac{28}{3}}}{2} = -1 \pm \frac{\sqrt{\frac{28}{3}}}{2}$$
Simplify the square root:
$$\sqrt{\frac{28}{3}} = \frac{2\sqrt{21}}{3}$$
So,
$$x = -1 \pm \frac{2\sqrt{21}}{3 \times 2} = -1 \pm \frac{\sqrt{21}}{3}$$
6. **Calculate approximate values:**
$$\sqrt{21} \approx 4.58$$
So critical points are approximately:
$$x_1 = -1 + \frac{4.58}{3} = -1 + 1.53 = 0.53$$
$$x_2 = -1 - 1.53 = -2.53$$
7. **Find the function values at critical points:**
Calculate $$f(0.53)$$:
$$f(0.53) = (0.53)^3 + 3(0.53)^2 - 4(0.53) \approx 0.15 + 0.84 - 2.12 = -1.13$$
Calculate $$f(-2.53)$$:
$$f(-2.53) = (-2.53)^3 + 3(-2.53)^2 - 4(-2.53) \approx -16.17 + 19.20 + 10.12 = 13.15$$
8. **Determine maxima and minima:**
Use the second derivative:
$$f''(x) = 6x + 6$$
Evaluate at $$x=0.53$$:
$$f''(0.53) = 6(0.53) + 6 = 3.18 + 6 = 9.18 > 0$$ so this is a minimum.
Evaluate at $$x=-2.53$$:
$$f''(-2.53) = 6(-2.53) + 6 = -15.18 + 6 = -9.18 < 0$$ so this is a maximum.
9. **Summary:**
- Maximum point at approximately $$(-2.53, 13.15)$$
- Minimum point at approximately $$(0.53, -1.13)$$
10. **Graph description:**
The cubic function has roots at $$x = -4, 0, 1$$.
It rises to a maximum near $$x = -2.53$$, then falls to a minimum near $$x = 0.53$$, and then rises again.
Final answer:
Maximum point: $$\boxed{(-2.53, 13.15)}$$
Minimum point: $$\boxed{(0.53, -1.13)}$$
Max Min Points
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